The invention relates to the diverless acquisition of data useful for determining the extent of cathodic protection of a portion of a structure immersed in salt-containing water and subject to corrosion, in particular, an offshore drilling or production platform. In one aspect, the invention relates to an improvement in a process for obtaining such data. In another aspect, the invention relates to an apparatus for the improved acquisition of such data. In a more particular aspect, the invention relates to improvements in apparatus and process for the obtaining of profiles of electrode potential versus depth in proximity with a portion of such structure under the surface of the sea and susceptible to corrosion. Such data are useful to determine the degree of protection afforded the structure by anodes affixed thereto, the necessity for attachment of additional anodes, the longevity of cathodic protection, and the like, all according to conventional engineering practice known to those skilled in the art.